The invention relates to a process for forming high density boron carbide compositions. More particularly, the invention relates to a process of forming high density boron carbide reacted with specified amounts of aluminum, and the products resulting from said process.
Methods of forming useful articles from boron carbide are well known in the art. The most widely used method, particularly when the resultant product is to have a high density, is that of hot-pressing. Because of the nature of boron carbide, hot-pressing to a high density requires temperatures in the neighborhood of 2300.degree. C and pressures of at least 1500 lbs. per sq. inch and preferably a pressure of 2500 lbs. per sq. inch, in an oxygen free atmosphere, usually after first preforming the shape by cold-pressing the boron carbide powder. Boron carbide fabricated in such a manner has been made into such artifacts as jet nozzles, turbine blades, sand blasting nozzles, wire drawing dies, mold liners, and the like and even more recently, armor plate for protecting personnel and equipment from ballistic projectiles. To fabricate high quality artifacts such as those mentioned above, the boron carbide powder is generally relatively pure, which inherently then, is relatively expensive.
More recent developments in the art, as disclosed in the Lowe U.S. Pat. No. 2,746,133, have brought forth improved boron carbide compositions. Higher strength jet nozzles, turbine blades, and the like have resulted from using boron carbide compositions reacted with 2 to 5% aluminum; such products exhibit higher strengths than the previously known boron carbide parts. Artifacts made from the boron carbide-aluminum composite system are more economical than the older essentially pure boron carbide products because the boron carbide-aluminum system does not require that the boron carbide be of as high purity as is required when boron carbide containing no additives is used. The process required, however, for fabrication of boron carbide-aluminum artifacts, is somewhat more complex than that used for straight boron carbide. The process of the Lowe Patent consists basically of a blending of boron carbide and up to 15% by weight of aluminum powder; hot-pressing at 1800.degree.-1900.degree. C under pressure of at least 500 psi to give a relatively low density piece; fragmentizing this hot-pressed piece and pulverizing the fragments in the presence of water to a particle size of approximately 15 microns for the purpose of eliminating aluminum carbide formed during the hot-pressing cycle; followed by hot-pressing of the so prepared powdered mixture of boron carbide, which now contains 2-5% aluminum, at a temperature of 1850.degree.-2325.degree. C under a pressure of not less than 1500 psi to produce a high-density boron carbide-aluminum product. Although this process produces highly useful products, it is a costly process in that it involves two high temperature hot-pressing steps and the necessary step of crushing and milling the product resulting from the initial hot-pressing step.